Production of unsaturated aliphatic nitriles

ABSTRACT

A process for the production of acrylonitrile by vapor phase catalytic ammoxidation of propylene at an elevated temperature over an oxide composition comprising antimony, vanadium and a polyvalent metal selected from tin, iron, cobalt, or titanium, in specified atom ratios.

United States Patent Barclay et al.

[ 51 Aug. 1, 1972 PRODUCTION OF UNSATURATED ALIPHATIC NITRILESInventors: John Lynn Barclay, Tadworth, England; Edward James Gasson,Dollar, Scotland; David James Hadley,

Tadworth, England Assignee: BP Chemicals Limited, London, En-

gland Filed: June 18, 1970 Appl. No.: 47,565

Related U.S. Application Data Continuation-impart of Ser. No. 719,258,April 5, 1968, abandoned.

Foreign Application Priority Data April 18, 1967 Great Britain..l7,7l7/67 U.S. Cl ..260/465.3 Int. Cl ..C07c 121/02 PrimaryExaminer-Joseph P. Brust Attorney-Ward, McElhannon, Brooks & Fitzpatrick[5 7] ABSTRACT A process for the production of acrylonitrile by vaporphase catalytic ammoxidation of propylene at an elevated temperatureover an oxide composition comprising antimony, vanadium and a polyvalentmetal selected from tin, iron, cobalt, or titanium, in specified atomratios.

4 Claims, No Drawings PRODUCTION OF UNSATURATED ALIPHATIC NITRILES Thisapplication is a continuation-impart of applicants parent applicationSer. No. 719,258 filed Apr. 5, 1968 and now abandoned.

The present invention relates to the production of unsaturated aliphaticnitriles and in particular to the production of acrylonitrile.

Processes for the production of acrylonitrile by the vapor phasecatalytic reaction of propylene, molecular oxygen and ammonia are known.The catalysts for use in such processes in general comprise compositionscontaining one or more polyvalent metals combined as a suitable compoundor oxide of the metal.

It has now been found that whilst hitherto known catalysts for thereaction of propylene, molecular oxygen and ammonia to produceacrylonitrile have appeared satisfactory on a laboratory or pilot plantscale on a commercial scale plant certain disadvantages have beenrealized. Thus in particular it has been found that the selectivity ofthe known catalysts varies according to the operating pressure and thatunder increased pressure in the catalytic reactor the selectivity willfall off.

It is an object of the present invention to provide a catalyst withwhich the selectivity does not vary to the same extent with varyingoperating pressures as with catalysts known hitherto.

Accordingly the present invention is a process for the production ofacrylonitrile which comprises reacting at an elevated temperature in thevapor phase propylene, molecular oxygen and ammonia over an oxidecomposition comprising antimony, vanadium and one or more additionalpolyvalent metals tin, iron, cobalt, or titanium, in proportion 1 gm.atom of antimony, 0. l2 to 0.5 gm. atoms of vanadium and 0.25 to 0.5 gm.atoms of each additional polyvalent metal.

The oxide composition catalysts of the present invention may be regardedeither as mixtures of antimony oxide and vanadium oxide with an oxide ofa polyvalent metal or metals or as oxygen-containing compounds ofantimony, vanadium and a polyvalent metal or metals; under the reactionconditions either or both forms may be present.

The catalysts may be prepared, for instance, by intimately mixing theoxides or compounds yielding the oxides on heating, or byco-precipitation of the oxides, hydrated oxides or insoluble salts, fromaqueous solution. The polyvalent metal oxide or compound may be addedduring or after the admixture of the antimony and vanadium oxides orcompounds. Compounds of antimony which may be used in the manufacture ofthe catalysts include antimony trioxide, antimony tetroxide, antimonypentoxide or mixtures of such oxides. Hydrated forms of the oxides mayalso be used, for instance, compounds such as are formed by the actionof the aqueous nitric acid on antimony metal. Particularly suitablecompounds of polyvalent metals for the preparation of the catalyst arenitrates or chlorides.

The proportions of the various components of the catalyst may varywithin the above defined limits.

It is preferred to give the catalyst a prior heat-treatment, forinstance at a temperature between 550 and l,lO cc. in a molecularoxygen-containing gas.

The reaction of propylene with oxygen and ammonia over the catalysts maybe carried out in any suitable manner, for instance as a fixed bedprocess in which the catalyst is used in the form of granules orpellets, or as a fluidized bed process, or as a moving bed process.

The proportion of propylene in the feed to the reaction may vary withinfairly wide limits, for example, between 1 and 20 percent by volume ofthe feed, and suitably between 2 and 10 percent by volume. It ispreferred to use between 5 and 8 percent by volume of propylene in thefeed.

The concentration of oxygen in the feed may also vary within 'moderatelywide limits, for example, between 1 and 20 percent by volume. The oxygenmay be diluted with inert gases, and may be for example, supplied asair.

The reaction is suitably carried out in the presence, as diluent, of agas which is substantially inert under the conditions of reaction, forexample, nitrogen, propane, butane, isobutane, carbon dioxide and steam.It is preferred to carry out the reaction in the presence of steam ormixtures of steam and nitrogen. The concentration of the steam may varywithin wide limits, for instance between l0 and 60 percent by volume ofthe feed.

The concentration of ammonia may also vary within moderately widelimits, for instance, between 2 and 10 percent by volume of the feed. Ifthe maximum yield of acrylonitrile on propylene is required, it isdesirable to use an excess of ammonia over propylene. For instance, thepreferred concentration of ammonia is about 5-6 percent by volume of thefeed where this contains 5 percent of propylene.

The reaction is carried out at an elevated temperature preferably below500 C., e.g., between 300 and 450 C.

The contact time, defined as the volume of catalyst divided by the flowof gas per second calculated at room temperature and pressure, may be,for example in the range 1-30 seconds.

The reaction may be carried out at atmospheric pressure, or at superorsub-atmospheric pressures. It is preferred to operate at a pressure of lto 5 atmospheres absolute. Surprisingly, it has been found that theselectivity of the catalysts used in the process of the presentinvention does not fall off with increasing reaction pressures as withcatalysts employed hitherto but in fact may increase with increasingpressure.

The acrylonitrile may be recovered from the reaction products in anysuitable manner, for example by extraction with water, preferably at anacid pH, followed by fractional distillation. In one method the hotreaction gases are contacted firstly with a cold dilute aqueous solutionof sulphuric acid which neutralises excess ammonia and extracts some ofthe nitrile, and secondly with cold water to extract the remainder ofthe nitrile; the nitrile is subsequently recovered from the extractionsby fractional distillation.

The process of the present invention is described in more detail withreference to the following examples.

EXAMPLE 1 Antimony trioxide powder (4,664 parts by weight) was addedduring 10 minutes to a stirred mixture of water (24,000 parts) andconcentrated nitric acid percent, 8000 parts) at 95l00 C. Powdered tinmetal (1,898 parts) was added to the stirred suspension over 30 minutes,the temperature being maintained at 95-100. Stirring was continued atthis temperature for 15 minutes and slurry centrifuged.

The catalyst cake from the centrifuge was resuspended in water (24,000parts) at 40 C and ammonia solution (one volume 0.880 in two vols water)added until the pH was 7.0. The slurry was stirred for a further 5minutes, the pH again readjusted to 7.0, and the slurry centrifuged. Thecake was resuspended in water (24,000 parts) at 40 and recentrifuged.

Vanadium pentoxide powder (1,456 parts) and graphite (80 parts) wereadded to the slurry and thoroughly mixed in. The wet paste was dried ontrays at 120 overnight and the powder pelleted to 5/32 in. rightcylinders and heated in a stream of air at 850 for 16 hours following acontrolled rise from 300 to 850 at 20 /hour.

The catalyst was loaded into a ft. X l in. reactor,

the inlet half of the catalyst charge being diluted with 45 percent v/vinert diluent. A feed gas composition of 5 percent propylene, 6 percentammonia, 60 percent air and 29 percent steam was fed to the reactorgiving a contact time of 4 seconds and an inlet pressure of 20 lbs. At abath temperature of 438, 63.9 percent of the propylene fed was convertedto acrylonitrile, 2.3 percent to acrolein, 7.3 percent to hydrogencyanide and 19 percent to carbon oxides.

EXAMPLE 2 Antimony trioxide powder (3,182 parts by weight) was addedduring 10 minutes to a stirred solution of water (12,000 parts) andconcentrated nitric acid (3,600 parts, 70 percent) at 95 -100. Powderedtin metal (860 parts) was added to the stirred suspension at 95-l00 over30 minutes, and stirring continued at this temperature for a furtherminutes and the slurry centrifuged.

The catalyst cake was resuspended in distilled water (16,000 parts) anda solution of ferric nitrate (1,469 parts) in water (2,000 parts) added.The pH of the stirred suspension was raised 7.0 at 40 C by the additionof ammonium hydroxide solution.

The slurry was stirred at 40 for a further 10 minutes and pH againreadjusted to 7.0, and then centrifuged. The cake was resuspended inwater (12,000 parts) for 30 minutes at 40 and recentrifuged.

Vanadium pentoxide powder (662 parts) and graphite (60 parts) were addedto the slurry and thoroughly mixed in. The wet paste was thoroughlydried on trays at 120 overnight, the powder pelleted to 5/32 in. rightcylinders, and heated in a stream of air at 850 for 16 hours following acontrolled rise from 300 to 850 at 20 /hour.

The catalyst was loaded into a 10 ft. X 1 in. reactor, the inlet half ofthe catalyst bed being diluted with 45 percent v/v inert diluent. A feedgas composition of 5 percent propylene, 6 percent ammonia, 65 percentair, and 24 percent steam was fed to the reactor giving a contact timeof 4 seconds and an inlet pressure of 20 p.s.i.g. At a bath temperatureof 447, 65.4 percent of the propylene fed was converted toacrylonitrile, L5 percent to acrolein, 7.6 percent to hydrogen cyanideand 19.8 percent to carbon oxides.

EXAMPLE 3 A pelleted (5/32in.) oxide catalyst containing antimony,vanadium and titanium in the atomic ratio (2:1:0.79) was prepared in thesame way as described in Example 1 except that an equivalent amount ofpowdered titanium metal was substituted for the powdered tin metal usedin Example 1.

The catalyst so prepared was loaded into a 10 ft. X A in. ID. reactorand fed with a gas feed consisting of ammonia, 6 percent v/v; propylene,5 percent air, 60 percent, and steam, 29 percent at 3.5 seconds contacttime (N.T.P.) and an inlet pressure of 12 p.s.i.g. At a temperature of470 the yields were: acrylonitrile 56.4 percent; acrolein 2.0 percent;hydrogen cyanide, 8.7 percent, carbon monoxide, 7.5 percent, and carbondioxide, 6.6 percent.

EXAMPLE 4 Cobalt nitrate hexahydrate (145 parts by weight) was dissolvedin water (300 parts by weight) and antimony trioxide (219 parts byweight) added. The mixture was vigorously stirred and sufficientammonium hydroxide (Sp.gr. 0.880) was added until a pH of 8.0 wasreached. The solid was then filtered off and dried to a cake.

Meanwhile, vanadium pentoxide (18.2 parts by weight) was stirred withwater by weight) at 50 C and dissolved by the addition of sufficientoxalic acid. The mixed antimony cobalt cake was then added to thevanadium oxalate solution and the whole mixture evaporated to dryness.After drying the residue for 12 hr. at C it was formed into one-eighthin. diameter tablets which were heated in an air stream, initially at100 C. The temperature was then raised to 800 C at the rate of 22!hr.and maintained at 800 C for 16 hr. The catalyst contained antimony,vanadium and cobalt in the atomic ration of 310.4:1 respectively.

The pelleted oxide catalyst was loaded in a reaction which is a glassU-tube of internal diameter 10 mm. immersed in a molten tin bath. A feedgas composition of 5 percent propylene, 6 percent ammonia, 54 percentair and 35 percent steam was preheated and fed to the reactor giving acontact time of 4.5 seconds and an inlet pressure of 10 mml-lg aboveatmospheric. At a bath temperature of 475C, a yield of 40 percentacrylonitrile based on the propylene fed was obtained at a selectivityof 51 percent based on propylene consumed.

What is claimed is:

l. A process for the production of acrylonitrile which comprisesreacting at an elevated temperature in the vapor phase propylene,molecular oxygen and ammonia over an oxide composition consistingessentially of oxygen, antimony, vanadium and tin in proportion 1 gm.atom of antimony, 0.12 to 0.5 gm. atoms of vanadium and 0.25 to 0.5 gm.atoms of tin.

2. A process for the production of acrylonitrile which comprisesreacting at an elevated temperature in the vapor phase propylene,molecular oxygen and ammonia over an oxide composition consistingessentially of oxygen, antimony, vanadium, tin and iron in proportion 1gm atom of antimony, 0.12 to 0.5 gm atoms of vanadium and 0.25 to 0.5 gmatoms each of tin and iron.

comprises reacting at an elevated temperature in the vapor phasepropylene, molecular oxygen and ammonia over an oxide compositionconsisting essentially of oxygen, antimony, vanadium and titanium inproportion 1 gm. atom of antimony, 0.12 to 0.5 gm. atoms of vanadium,and 0.25 to 0.5 gm. atoms of titanium.

I I I I 1

2. A process for the production of acrylonitrile which comprisesreacting at an elevated temperature in the vapor phase propylene,molecular oxygen and ammonia over an oxide composition consistingessentially of oxygen, antimony, vanadium, tin and iron in proportion 1gm atom of antimony, 0.12 to 0.5 gm atoms of vanadium and 0.25 to 0.5 gmatoms each of tin and iron.
 3. A process for the production ofacrylonitrile which comprises reacting at an elevated temperature in thevapor phase propylene, molecular oxygen and ammonia over an oxidecomposition consisting essentially of oxygen, antimony, vanadium andcobalt in proportion 1 gm. atom of antimony, 0.12 to 0.5 gm. atoms ofvanadium, and 0.25 to 0.5 gm. atoms of cobalt.
 4. A process for theproduction of acrylonitrile which comprises reacting at an elevatedtemperature in the vapor phase propylene, molecular oxygen and ammoniaover an oxide composition consisting essentially of oxygen, antimony,vanadium and titanium in proportion 1 gm. atom of antimony, 0.12 to 0.5gm. atoms of vanadium, and 0.25 to 0.5 gm. atoms of titanium.